Pectin, along with cellulose, hemicellulose, and lignin, constitute the major components of plant tissue. The cellulose, hemicellulose and lignin portions are located within the cell structure where they provide support to the cell. The pectic portion is located between cells where it acts as a biological adhesive to hold the cells together.
Pectin is a water soluble, branched polysaccharide consisting of D-galacturonate units joined by .alpha.-1,4 glycosidic bonds interrupted with 1,2 L-rhamnose residues. The neutral sugars D-galactose, L-arabinose, D-xylose, and L-fucose form side chains from the .alpha.-1,4 glycosidic backbone. The .alpha.-1,4 glycosidic backbone includes about 5-10% by weight methylated carboxyl groups and about 5-10% by weight alpha acetyl groups. The molecular weight of pectin varies greatly from about 20,000 for sugar beet pectin up to about 200,000 for apple and citrus pectins.
Refined pectin is generally extracted from plant tissue, such as citrus pulp, by (i) treating the plant tissue with an acid (pH less than about 2) or base (pH greater than about 10) until the pectin component of the tissue is separated from the other components, (ii) solubilizing the free pectin, (iii) separating the pectin-containing liquid from the pectin-depleted solids, and (iv) precipitating the pectin by addition of a hydrocarbon precipitating agent, such as an alcohol.
Refined pectin is widely used in the food industry as a gelling agent. However, the high cost of refined pectin has limited the extent to which pectin is used. While the pectin-producing industry has long recognized the need for a low-cost, food-grade pectin product, efforts to produce such a crude pectin product has meet with limited success.
Grindsted (PCT Publication 91/15517) discloses a gelling composition comprising a crude fiber, such as carrot fiber, which has been (i) heat treated with acid, such as hydrochloric acid, at a pH of about 1-3 to convert insoluble pectin in the fiber to soluble pectin, (ii) treated with a base, such as calcium hydroxide, to increase the pH of the fiber to about 3-8, and then (iii) dried by evaporative methods to form a dry, pectin-containing fiber product.
While the process of Grindsted is significantly less expensive that the process used to produce fully refined pectin, the Grindsted process is slow (requires the fiber to be treated with an acid for several hours to achieve appreciable conversion of the pectin), requires the use and disposal of substantial quantities of environmentally hazardous acids, and requires the use of a considerable amount of energy to evaporatively dry the pH treated fiber.
Accordingly, a substantial need still exists for a simple, low-costs environmentally-friendly method for producing a pectin-containing fiber product possessing the gelling characteristic of refined pectin.